The adverse effects of ultraviolet rays have drawn attention in the recent years. Thus, various kinds of sunscreen cosmetics have been developed. For example, there are known sunscreen cosmetics having a form such as water-in-oil type, oil-in-water type and solvent type.
Among these, the sunscreen cosmetics of water-in-oil type or solvent type have generally good water resistance, since oil components or solvents contained in the composition make a continuous phase to form a cosmetic film with hydrophobicity when applied to the skin.
However, since these cosmetics sometimes provide a heavy greasy sensation and poor spreadability when applied to the skin, they are not suitable as a cosmetic to be used during the hot and humid midsummer when they are used with high frequency.
Further, these cosmetics have an inconvenience that the cosmetic film formed thereby is difficult to be completely removed without using a special make-up remover due to its hydrophobicity.
In contrast, sunscreen cosmetics in the form of an oil-in-water emulsion in which water makes a continuous phase are excellent in freshening texture and spreadability when applied to the skin. However, sunscreen cosmetics containing an oil-soluble ultraviolet absorber need a large amount of hydrophilic surfactant for dispersing the oil-soluble ultraviolet absorber. Therefore, such sunscreen cosmetics have a drawback that they are insufficient in durability as a cosmetic film due to their affinity for sweat and water. Thus, it has been eagerly desired to develop cosmetics in the form of an oil-in-water emulsion which retain the good freshening texture and have good durability as a cosmetic film, and various kinds of proposals concerning such cosmetics have been provided to date.
For example, Patent literature 1 discloses oil-in-water emulsion compositions containing a complex obtained by mixing an ampholytic surfactant and/or a semi-polar surfactant and a higher fatty acid, a powder, water and a non-volatile oil component. These oil-in-water emulsion compositions contain a liquid non-volatile oil component, such as dimethyl polysiloxane, to improve water resistance. These compositions raise a problem that the emulsions become unstable when a large amount of oil-soluble ultraviolet absorber with high polarity is incorporated to enhance ultraviolet protection efficacy. Also, the compositions are still insufficient in water resistance.
Further, Patent literature 2 proposes oil-in-water emulsion compositions containing a powder coated with a polymer composed of specified monomers having carboxyl groups and a basic compound both of which are dispersed in an aqueous phase. These cosmetic compositions are designed to make metal oxides, which are used as an agent for scattering ultraviolet rays, disperse stably in an aqueous phase and to improve water resistance. These cosmetic compositions differ in composition from emulsion compositions containing an oil-soluble ultraviolet absorber. Further, Patent literature 2 discloses that addition of a higher fatty acid is not preferable since the higher fatty acid neutralizes a basic compound so as to form a salt of higher fatty acid that significantly deteriorates water resistance (refer to paragraph [0038]).
Further, Patent literature 3 proposes oil-in-water emulsion cosmetics for sunscreen containing (A) a higher fatty acid, (B) a higher alcohol, (C) a glycerin derivative and (D) a ultraviolet absorber, being free of a hydrophilic surfactant, and having a pH of from 5.0 to 7.0. The Patent literature 3 discloses that oil-in-water emulsion cosmetics with good stability can be obtained without using a hydrophilic surfactant, and that the cosmetics have mild acidity, very weak irritation to the skin, high water resistance, good resistance for water and sweat and good durability of cosmetic film during the hot and humid midsummer and upon exercising (refer to paragraph [0034]). But, the Patent literature 3 discloses that these compositions need to contain the (A) higher fatty acid, the (B) higher alcohol and the (C) glycerin derivative in a specified proportion and that, where emulsion compositions are free of the (B) higher alcohol or the (C) glycerin derivative, stable emulsion compositions cannot be obtained due to insufficient emulsifying capacity (refer to comparative examples 1 and 2). Also, the Patent literature 3 discloses that emulsion compositions prepared by using the (A) higher fatty acid and a nonionic surfactant exhibit weak alkalinity, weak irritation to the skin and insufficient water resistance (refer to comparative example 7).